(1) Field of the Invention
The present invention relates to a process for controlling combustion of burners attached to a furnace such as a firing kiln and an apparatus therefor.
(2) Related Art Statement
In order to control combustion of burners, it was conventionally a common process to proportionally control the output of each burner depending upon a temperature inside a furnace in the state that burning is continuously being effected through all burners. However, if burning is effected through the burners in the state that combustion output is throttled, an amount of a combustion gas is lacking, and the temperature distribution in the furnace largely varies. Consequently, a large amount of air needs to be forcedly fed into the furnace even in the state that the combustion output is throttled. An increased amount of fuel for the burners needs is required to heat the fed air.
In order to solve the above problem, a burner combustion-controlling process has been developed, which can control the temperature inside the furnace without throttling the combustion output through each of the burners. According to this process, the interior of the furnace is divided into a plurality of control zones, burners are arranged in the respective control zones, and successively subjected to combustion for a short time, while the control zones are successively employed as a combustion zone, and such a combustion cycle is repeated. FIG. 6 shows this process in the form of a time chart. For example, the interior of the furnace is divided into three control zones at upper, middle and lower stages. The upper stage burner is subjected to combustion for the first 6 seconds, then the middle stage burner is subjected to combustion for the next 6 seconds, and the lower stage burner is thereafter subjected to combustion for the succeeding 6 seconds, as represented in plots (A), (B) and (C), respectively. This cycle is repeated. Since each burner is subjected to combustion, although intermittently, without throttling its combustion output, this process has an advantage in that a large amount of air need not be fed inside the furnace. Further, the amount of generated heat through all the burners can be controlled by adjusting a time period from a point of time at which combustion through a certain stage burner is stopped to a point of time at which combustion is successively started through another stage burner.
On the other hand, it was clarified that when the above burner combustion-controlling process was applied to an actual furnace, the following problem occurred. That is, according to this burner combustion-controlling process, the burners in all the control zones are subjected to combustion in the same pattern depending upon the temperature inside the furnace. Thus, as shown in FIG. 7, it may happen that when the middle stage temperature approaches a preset temperature, the temperature in the upper stage section exceeds its preset temperature. As is understood from this, it was clarified that the above conventional intermittent burner combustion-controlling process cannot exhibit sufficient effect in reducing variations in the temperature distribution inside the furnace.